This invention is directed to electronic musical instruments generally and, more particularly, to an electronic musical instrument including an electronic sound reverberation system.
Sound reverberation is provided in electronic musical instruments to simulate the acoustical effects of a large auditorium or concert hall in a much smaller listening area. In the concert hall or other similar large listening area, sounds reach the listener both by a direct unimpeded transmission path and by reflection from all the various surfaces within the area. These reflected signals are attenuated in varying amounts due to the nature and characteristics of the reflecting surfaces and since each reflected sound wave travels a different distance to reach the listener each is delayed a different amount of time. All of these acoustic signals, both direct and reflected, blend together for a full, pleasing sound for listeners.
Artifical sound reverberation was initially provided via mechanical spring reverberators. These mechanical reverberators generally consist of pairs of springs with slightly different time delays. The reverberator springs are driven at one end by an electrical to mechanical transducer and the delayed mechanical motions are received by a mechanical to electrical transducer at the other end which converts the mechanical movement back into signals representative of the original sounds but delayed in time. Mechanical sound reverberators suffer from numerous problems. They are easily effected by external mechanical vibration which produce spurious wounds, the quality of reproduction and delay times are effected by ambient conditions, the frequency range is generally limited to the lower frequencies of audible sound and the delay time is fixed rendering the reverberated sound repetitive and unnatural.
Various techniques have been developed for use with mechanical reverberators to attempt to overcome these problems. These techniques include the use of multiple delay lines, filtering and frequency shifting, the latter to attempt to improve the frequency response of the mechanical reverberators. While these modifications have extended the versatility of mechanical reverberators, they require either additional mechanical elements which increase the size, weight and assembly time of the mechanical reverberators or additional circuitry which is often times complicated and expensive. Furthermore, such modifications of mechanical reverberators have not completely solved the problems associated with mechanical sound reverberation.
More recently all electronic reverberators have been introduced. Electronic sound reverberation units include electric charge transferring devices which are used to set delay times to produce sound reverberation similar to the mechanical reverberation units. Digital techniques have also been employed wherein an analog signal is converted to a digital signal, passed through digital delay lines or shift registers and reconverted to an analog signal to provide the delayed time periods required for sound reverberation. None of the presently available sound reverberators provide a true and natural reverberated sound composed from the colorations and intermingling of sounds which are produced by sound waves reflecting from various surfaces at varying distances from the sound stage in a large auditorium or concert hall.